KECENT PROGRESS IN PHYSICS. 



3S5 



Now, If I = 1.18 and VVi* = l-l^, that is, the two quotients are 



nearly equal, or -=- = ~- ; moreover, 1^1= 1.27 and ^-AM = 1.35, 



vd' Y" , . o , 



or very nearly —=—= :^, ; and, finally, i|| = 1.16, and M| =: 



V^'" Y" 

 1.17, or — =- =: — , therefore the values of Y are nearly In the in- 



Va' Y'" 



verse ratio of the square roots of the corresponding thiol', nesses of the 

 glass ; that is 



Vd = Y 



or 



but we have J =2 c Y"^, hence 



d~^ 



d X J = c. p, 



or 



J = 



_ cjo- 



d 



that is, tJie intensity of the spark is inversely proportional to the thick- 

 ness of the condenser. 



The rediaining experiments which Masson made on this point did 

 not coincide generally so well with the above deductions. This he 

 ascribes to the circumstance that he could not measure the thickness 

 of the glass with sufficient accuracy, and that the different condensers 

 may have had unequal "capacities for condensation." 



§ 93. Injiuence of the nature of the pole on the electrical sparh. — Mas- 

 son found that the spark is somewhat more intense, if, under circum- 

 stances otherwise the same, it be passed between lead, zinc, and tin 

 balls, than when the balls (equal, in size) are of copper, brass, or iron. 

 Masson thinks that this depends upon the unequal tenacity of the 

 metals. In all his experiments there were traces of a transportation 

 of the metal from one pole to the other ; now since lead, for example, 

 is less tenacious than copper, more lead will be carried off than copper 

 with the same tension of the electricity ; the conducting circuit then 

 will have its capacity for conduction suddenly increased, and the light 

 must become more brilliant in consequence. 

 25 s 



